In an engine of an electronically-controlled fuel injection system, various data representing the operational condition thereof are obtained from sensors to control an injector (fuel injection valve) on the basis of these data, supply a fuel at a required feed rate and thereby maintain a predetermined air-fuel ratio thereafter called "the A/F."
To constantly maintain the correct A/F even when the properties of actuators for various sensors and an injector are very randomly, or vary with the lapse of time, a method of detecting an output A/F in an engine with an A/F sensor, such as an O.sub.2 sensor, and then carrying out a closed loop control operation based on a feedback control operation has been used.
However, in this conventional closed loop A/F control system, response is delayed considerably, so that the A/F cannot be controlled in a transitional region in which the operating condition of the engine varies.
With a view to eliminating these inconveniences, an engine control device of the so-called learing control system has been proposed, which is shown in, for example, FIG. 4 in Japanese Patent Laid-Open No. 57029/1979 dated May 8, 1979. This engine control device is adapted to successively store control correction rates while the A/F is subjected to a closed loop control based on feedback control, and read these stored control correction rates and reflect them in an A/F control in a transitional region so that a proper A/F can be obtained even when the engine is in a transitional operational region.
A/F sensors including an O.sub.2 sensor do not perform adequately in the full-load region of operation when the throttle is almost completely open. Therefore, it is necessary to interrupt closed loop A/F control which is based on a feedback control operation in the region of full-load operation. This conventional engine control device can not control an engine if results of closed loop A/F control based on feedback are reflected, in all operational regions of the engine.
An object of the present invention is to provide an engine control device which can reflect the results of closed loop A/F control based on feedback, sufficiently and accurately in all operational regions of an engine, and which can maintain an accurate A/F at all times.
As will be made clear, the present invention is characterized in that closed loop A/F control based on feedback, is applied to the property correction of a sensor which is adapted to measure the flow rate of a suction gas in an engine, to thereby expand these regions in which the results mentioned above are reflected.